list - 如何在Prolog中将split/3转换为split/4？

Question

以下代码适用于split_list/3:

split_list([], _, [[],[]]).
split_list(T, 0, [[],T]).
split_list([H|T], N, [[H|Y],Z]) :-
   N1 is N-1,
   split_list(T, N1, [Y,Z]).

例如:

?- split_list([a,s,d,f,g,h,j], 3, R).
R = [[a, s, d], [f, g, h, j]] .              % observed answer

但是，我想将 split_list/3 转换为 split/4:

?- split([a,s,d,f,g,h,j], 2, R1, R2).
R1 = [a,s], R2 = [d,f,g,h,j].                % expected answer

怎样才能得到我想要的答案？有什么建议么？谢谢:)

Answer 1

这是 split/4 的直接定义:

split(AsBs, N, As, Bs) :-   append(As, Bs, AsBs),   length(As, N).

Sample query as given by the OP:

?- split([a,s,d,f,g,h,j], 2, R1, R2).
   R1 = [a,s], R2 = [d,f,g,h,j]
;  false.

如何概括上述查询？

?- split([a,s,d,f,g,h,j], I, R1, R2).
   I = 0, R1 = [],              R2 = [a,s,d,f,g,h,j]
;  I = 1, R1 = [a],             R2 =   [s,d,f,g,h,j]
;  I = 2, R1 = [a,s],           R2 =     [d,f,g,h,j]
;  I = 3, R1 = [a,s,d],         R2 =       [f,g,h,j]
;  I = 4, R1 = [a,s,d,f],       R2 =         [g,h,j]
;  I = 5, R1 = [a,s,d,f,g],     R2 =           [h,j]
;  I = 6, R1 = [a,s,d,f,g,h],   R2 =             [j]
;  I = 7, R1 = [a,s,d,f,g,h,j], R2 =              [].